1. Field of the Invention
This invention relates to LED-based (Light Emitting Diode-based) lamps and in particular, although not exclusively, to linear lighting bars for use in a display cabinet or refrigerated cabinet. The invention further concerns a panel lamp and light emitting sign utilizing one or more such lamps.
2. Description of the Related Art
White light emitting LEDs (“white LEDs”) are known in the art and are a relatively recent innovation. It was not until high brightness LEDs emitting in the blue/ultraviolet (U.V.) part of the electromagnetic spectrum were developed that it became practical to develop white light sources based on LEDs. As taught, for example in U.S. Pat. No. 5,998,925, white LEDs include one or more phosphor materials, that is photo-luminescent materials, which absorb a portion of the radiation emitted by the LED and re-emit radiation of a different color (wavelength). Typically, the LED chip generates blue light and the phosphor material(s) absorbs a percentage of the blue light and re-emits yellow light or a combination of green and red light, green and yellow light or yellow and red light. The portion of the blue light generated by the LED that is not absorbed by the phosphor material combined with the light emitted by the phosphor material provides light which appears to the eye as being nearly white in color.
Due to their long operating life expectancy (>50,000 hours) and low power consumption high brightness white LEDs are increasingly being used to replace conventional light sources such as fluorescent, compact fluorescent and incandescent bulbs. Today, most lighting fixture designs utilizing white LEDs comprise systems in which a white LED (more typically an array of white LEDs) replaces the conventional light source component. Moreover, due to their compact size, compared with conventional light sources, white LEDs offer the potential to construct compact lighting fixtures.